Conventionally, there is a technical field of imaging lenses where a short overall length and low price are demanded for use in lens modules for image acquisition that are mounted in relatively thin equipment, such as simple digital cameras, webcams for personal computers, and portable imaging systems in general. In order to satisfy this demand, previous imaging lenses have been formed in a one-piece lens construction. Because the electronic image sensing chips previously used with the lens modules were compact and had low resolution, maintaining a small image size on the image sensing chips and miniaturizing the lens systems with a small number of lens components was a priority. In previous arrangements, even with a one-piece lens construction, aberrations were acceptable and the incidence angle of light rays onto the image sensing chip was not so large as to be a problem.
However, in recent years, because the resolution and the size of the image sensing chips have increased, aberrations occurring in one-piece lenses are too large to achieve the desired optical performance. Therefore, it has become necessary to develop a lens system with a short overall length and with an optical performance that matches image sensing chips having enhanced resolution and size. Also, because when using such an image sensing chip, the principal rays need to be incident nearly normal onto the surface of the image sensing chip for all rays that are incident onto the chip, the imaging lenses need to be redesigned for the newer, larger image sensing chips.
The present invention relates to a compact imaging lens having a small number of lens components and a short overall length. More particularly, the present invention relates to an imaging lens for use with personal computers, and portable imaging systems in general, that has a high optical performance even with new, larger, higher resolution image sensing chips, and to an imaging lens that reduces the angle of incidence of light rays onto such an image sensing chip.